Indirectly Heated, Storage Water Heater System

ABSTRACT

A system is shown for providing domestic hot water for potable use. The energy source is a steam powered heat exchanger. Water is heated in a heat engine package including the heat exchanger, a temperature operated pump and a condensate control valve. The heat package works in conjunction with a water storage package including a water storage tank and an electronic controller which controls the operation of the pump and condensate control valve. The electronic controller is operated so that the control of steam supplied to the system and flow of water through the heat exchanger ensures that steam is only present in the heat exchanger when there is a predetermined high flow rate of water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a storage type water heater system with a storage tank that is indirectly heated by a steam heat source, the system being used to provide domestic hot water for potable uses.

2. Description of the Prior Art

Water heaters are used in a large variety of residential, commercial and industrial settings. For example, large storage tank systems are often found in hospitals and institutions, industrial plants, schools, universities, apartment complexes, and the like. The different types of water heaters which are used to supply hot water to these systems may use various sources of energy, such as gas, oil, electricity or steam. For example, in conventional gas/oil fired water heaters, hot gas flows through a series of vertically mounted tubes which are mounted in vertical fashion between top and bottom support plates within the water heater tank. Water flows into and out of a chamber located between the support plates and contacts and circulates about the exterior of the vertical tubes to effect heat transfer to heat the water.

U.S. Pat. No. 4,465,024, issued Aug. 14, 1984, and assigned to the assignee of the present invention describes another type of water heater which has a submerged, pressurized combustion chamber so that all combustion occurs in the water heater tank interior in a chamber surrounded by water, thereby reducing heat loss and increasing efficiency. These two examples are merely intended to be illustrative of the various types of gas/oil fired water heaters which exist in the prior art.

In some of the end applications mentioned above, such as, for example, in a municipal apartment complex or an industrial process, it may be more convenient and economical to utilize an existing source of steam or other hot fluid as the energy source for heating the water, rather than using gas or oil. There are a large number of prior art patents on devices in which liquids have been heated by fluids such as steam or other hot liquids. One of the common apparatus designs is the so called “shell-and-tube” heat exchanger. In conventional shell-and-tube heat exchangers, the tube section of the heat exchanger consists of a bundle of tubes which are open at both ends. At each end, the tubes extend through and are welded to a tube sheet. The shell of the heat exchanger completely encloses the bundle. The tubes within the bundle are spaced apart from each other, and from the shell, to define the shell-side section of the heat exchanger. In a typical heat exchanging operation, one of the fluids (liquid or gas) is passed through the tube section of the heat exchanger. The other fluid is then passed through the shell section, that is, on the outside of the tubes, often in a flow path which is countercurrent to the fluid flowing through the tube section.

Because the demand for hot water tends to vary over time in most installations, it is generally necessary to provide some sort of control over the heat source or flow rate through the device to accommodate the varying flow rates of the water being heated. In most applications the temperature of the water to be heated varies dramatically according to the time of year, and other factors. For example, a typical domestic hot water system is only under demand about 10-20% of the time. Additionally, in most applications the quantity of water flowing through the heat exchanger varies according to the time of day and use patterns of the application. Thus, the heat exchanger outlet water temperature must be regulated in order to accommodate variability resulting from the inlet water temperature and flow rate changes. In the case of hot water storage systems utilizing bulk storage tanks, one type of existing control system is commonly referred to as the “feedback-type” system. These systems operate by sensing the temperature of the water in the storage tank, using a temperature sensing device in the tank to provide instructions to a steam control valve. However, steam control valves of this type tend to be quite expensive, adding significantly to the overall cost of such systems.

Thus, despite the improvement in the art generally in the area of heat exchangers and water heaters of the above type, a need continues to exist for an improved water heater design which utilizes steam from a local boiler or district plant to provide energy to heat water to a desired temperature for a variety of hot water end use applications and which solves many of the problems discussed above.

SUMMARY OF THE INVENTION

A system is shown for providing potable, domestic hot water using an indirectly heated, storage water heater system. The energy source is district/municipal or locally produced steam at pressures up to 125 psig. The water is heated in a heat engine package which includes a steam operated heat exchanger, a temperature operated pump and a condensate control valve in conjunction with a storage package including a water storage tank with an internal temperature sensor, the water storage tank being located apart from but plumbed to the steam operated heat exchanger. The storage package also has operatively associated therewith an electronic controller which communicates with the internal temperature sensor in the water storage tank, the temperature operated pump, and the condensate control valve to control the supply of steam to the heat exchanger and the discharge of condensate therefrom, as well as the flow of hot and cold water to and from the water storage tank. The commercial version of the system has all related safeties for ASME IV Part HLW and recommended safety controls for a potable water heating device.

Although a variety of heat exchanger designs could be utilized, the steam operated heat exchanger can conveniently be of the shell and tube heat exchanger design, as has briefly been described, with a shell side and a tube side, with relatively cooler water to be heated being passed on a selected one of the shell and tube side of the heat exchanger and steam being passed on a remaining side of the heat exchanger, the steam being supplied from a suitable steam source.

The preferred water storage tank has an interior, a cold water inlet and a cold water circulation outlet connected by a conduit to one side of the shell and tube heat exchanger. A hot water circulation return inlet located within the tank interior is also plumbed to the heat exchanger for directing an inlet stream of hot water from the steam operated heat exchanger back into the storage tank interior. Hot water is discharged from the tank interior at a hot water outlet. Preferably, a diffuser nozzle is located within the tank interior at both the cold water inlet and the hot water circulation return inlet to reduce velocity and directionality of the water being introduced into the tank interior and disperse the stream flows into the tank. Flows out of the tank will inherently have low turbulence. The presence of the diffuser nozzles prevents disturbing a naturally occurring stratification of heat, providing a more uniform tank temperature as well as ensuring the heat exchanger is provided with the coldest inlet water, thereby increasing the efficiency of the system. Preferably, the diffuser nozzles are mounted on the tank by means of a bolt-on flange located on an exterior surface of the water storage tank. The bolt on flange fitting facilitates ease of maintenance and cleaning of the tank interior and diffuser nozzles.

The electronic controller is operated so that the control of steam supplied to the system and flow of water through the heat exchanger ensures that steam is only present in the heat exchanger when there is a predetermined high flow rate of water. In brief:

-   -   Demand for hot water causes cold water to flow into the heat         exchanger.     -   When the control sensor drops below a predetermined set point         temperature, the circulation and heating systems are energized.     -   While the system is heating, and demand is occurring, the         circulation system blends cold water from the cold water inlet         is with water from the coldest part of the tank interior by the         circulation system. This blended water flows through the heat         exchanger and returns to the tank heated.     -   When demand (flow) stops, and the control sensor remains below         the set point temperature, the circulation system will continue         to circulate water from the coldest part of the tank interior         though the heat exchanger, returning heated water to the         interior of the tank. This standby heating mode of operation         continues to occur until the tank again reaches the set point         temperature.

A method is also shown for operating the previously described indirectly heated, storage water heater system. In an initial state, the heat exchanger, water storage tank and associated plumbing are at ambient or ground water temperatures and wherein the system is first subjected to a startup cycle in which power is applied to power the system and provide a control signal for the water heating system's operation. Once it has been determined that the system is full of potable water and air has been removed from the water storage tank, steam is then supplied to the heat engine. When power is supplied to the electronic controller, a temperature sensor associated with the controller, which is located in the storage tank interior, senses that water in the water storage tank is below a given set point. The electronic controller then supplies power to the temperature operated circulating pump and to the condensate control valve beginning circulation flow to the heat engine and opening the condensate control valve.

Water is then circulated at a predetermined flow rate to the heat exchanger to extract latent heat from the steam being supplied to the heat exchanger, while also providing a relatively small degree of sub-cooling, thereby causing a flow of condensate on the steam side of the heat exchanger while drawing more steam through the system. Circulating water returns to the water storage tank interior through the hot water circulation return inlet and diffuser nozzle, causing the temperature of water in the water storage tank to rise.

The use of the diffuser nozzle causes stored water to fill from a top region of the water storage tank until the temperature sensor located in the tank interior reaches a desired set point. Once the desired set point is reached, the electronic controller immediately removes power from the condensate control valve as the circulating pump continues to run on a time delay shutoff.

The steam operated heat exchanger has internal heating surfaces, and wherein continued running of the circulating pump causes the heat exchanger to flood with condensate until all heating surfaces are in contact with the condensate, the condensate then being cooled below the point of scale formation. Once the predetermined time delay has been reached, power is removed from the circulating pump and the system is in a standby state.

As supplied domestic potable water is used, cold water flows into the water storage tank interior through the cold water inlet diffuser, the relatively colder water entering the diffuser causing water to fill the tank from a bottom region to a top region. When the level of cold water in the tank reaches a location of the electronic controller temperature sensor, the electronic controller will provide power to the circulating pump and condensate control valve, beginning the heating cycle again.

The operation of the water heater is inherently safe. Should a failure of the pump occur, no water will be circulated through the heat exchanger. While the water in the heat exchanger will be heated by the steam, an integral heat trap will prevent its introduction into the storage tank. In the event of a failure of the electronic controller, neither the pump nor condensate control valve will receive power. In addition, the system can be provided with is an upper temperature safety that will prevent the water from being heated to unsafe levels as well as a high temperature limit as required by UL safety standards. The heat exchanger itself can conveniently be of the double wall design to prevent cross contamination in the event of a tube leak and can be provided with a leak detection port for quick identification and repair of the system. The electronic controller can be equipped for communications with building automation systems and can be remotely monitored to inform of an alarm condition.

The heat engine and storage packages can be placed together and connected with factory plumbing. However, the two part design allows for the heat engine to be located remotely from the storage tank through field plumbing with no intermediate shutoffs or restrictions. This design allows for flexibility of the footprint in various boiler room configurations.

Additional objects, features and advantages will be apparent in the written description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, partially schematic view of the indirectly heated, storage water heater system of the invention.

FIG. 2 is view similar to FIG. 1 but showing the system during the call for heat phase of operation in which heat transfer is taking place.

FIG. 3 is a view similar to FIG. 2, showing the system as the call for heat ends, as well as the condensate control system operation.

FIG. 4 is a flow chart showing the steps in the electronic control system operation.

FIG. 5A is a perspective view of the diffuser tube used in the water storage tank of the system.

FIG. 5B is a side view of the diffuser tube.

FIG. 5C is a bottom view of the diffuser tube isolated from the mounting flange, showing the three rows of holes in the bottom surface of the tube.

DETAILED DESCRIPTION OF THE INVENTION

The preferred version of the invention presented in the following written description and the various features and advantageous details thereof are explained more fully with reference to the non-limiting examples included and as detailed in the description which follows. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the principal features of the invention as described herein. The examples used in the description which follows are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those skilled in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the claimed invention.

FIG. 1, is a partly schematic illustration of the principle components of the indirectly heated, storage water heater system of the invention. The term “storage water heater” is a term familiar to those skilled in the relevant arts and is used to describe water heater systems of the tank type typically consisting of a cylindrical vessel or container that keeps water continuously hot and ready to use. Compared to tankless heaters, storage water heaters have the advantage of using energy (gas or electricity) at a relatively slow rate, storing the heat for later use. Tankless water heaters—also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters—are also known in the art. These devices, as opposed to the storage water heaters described, instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil.

FIG. 1 illustrates the system of the invention which is used to provide potable, domestic hot water using an indirectly heated, storage water heater system. As will be explained in greater detail in the description which follows, the system includes a heat engine package comprising a steam operated heat exchanger, a temperature operated pump and a condensate control valve. The system also includes a companion storage package including a water storage tank with an internal temperature sensor, the water storage tank being located apart from but plumbed to the steam operated heat exchanger, and an electronic controller operatively associated with the temperature sensor in the water storage tank, the temperature operated pump, and the condensate control valve to control the supply of steam to the heat exchanger and the discharge of condensate therefrom, as well as the flow of hot and cold water to and from the water storage tank.

With reference to FIG. 1, the heat engine package includes a heat exchanger 11 which, in this case, is a shell and tube heat exchanger, of the type previously described, although other types of steam operated heat exchangers could be used as well. For example, while the water flow is shown as flowing on the tube side with the steam flowing on the shell side in FIGS. 1-3, the flows could be reversed with the steam filling the tube side of the exchanger and the colder water filling the shell side of the exchanger. In fact, any heat exchanger allowing for the control system to flood the exchanger and return to normal operation on a call for heat would be potentially usable.

In the preferred example shown in FIG. 1, the heat exchanger 11 is a generally cylindrical tank having an exterior sidewall 12 and an interior 14, and has a shell side 13 and a tube side 15. The heat exchanger is most preferably a double-wall, copper shell and tube exchanger with single-pass, counterflow design. It should be noted that no control valve is necessary if the system is supplied with 15 psi or lower steam pressure. In this example, relatively cooler water to be heated is passed on the tube side of the heat exchanger (as shown in FIG. 2), with steam from a suitable source entering at an inlet 17 and passing downwardly on the shell side of the exchanger in countercurrent flow. The heat exchanger is in communication with the storage tank 25 by means of cold water line 33 and hot water line 39.

A condensate line is provided to pass steam condensate through a condensate control valve 21 to a float and thermostatic (F&T) steam trap 23. These type of steam traps are known in the industry and keep steam from passing by. They are normally closed automatic valves that work like ballcocks. The F&T trap in the present system controls condensate and steam flow during on and off cycles of the system.

The heat exchanger can be provided with other conveniences. For example, the hot water conduit 39 can be equipped with a conventional relief valve 24. Clean-in place fittings 26, 28, can be provided on both the hot water return line 39 and the cold water line 33 to allow maintenance workers to clean the heat exchanger by flushing the exchanger with water or cleaning fluids as necessary without any system piping disassembly. The cold water line 33 and hot water line 39 are both equipped with on/off valves 34, 36.

The storage package of the system includes a water storage tank 25 having an interior 27, a cold water inlet 29, and a cold water circulation outlet 31 that is connected by a cold water conduit 33 to one side of the shell and tube heat exchange 11. In the example, the cold water conduit 33 communicates with the tube side 15 of the heat exchanger. A hot water circulation return inlet 35 is provided for directing an inlet stream of hot water from the steam operated heat exchanger back into the storage tank interior 27. A bronze pump 37 is sized to provide proper flow through the heat exchanger and back to the storage tank 25, as necessary, by circulating fluid through the cold water conduit 33 and hot water conduit 39, respectively. The storage tank is also equipped with a hot water outlet 41 and a conventional pressure relief valve 43.

A pair of diffuser nozzles 45, 47, are located within the tank interior 27 at both the cold water inlet 29 and the hot water circulation return inlet 35 to reduce velocity and directionality of the inlet water streams being introduced into the tank interior. The diffuser nozzles 45, 47, are identical, one of which is shown in greater detail in FIGS. 5A-5C. As shown in FIG. 5A, the diffuser nozzle 45 has an elongated, tubular cylindrical body 48 which has three sets of longitudinally aligned holes 49, 51, 53, which run along an underside location on the tubular body. The diffuser nozzles 45, 47, are preferably mounted on the exterior surface of the storage tank by a bolt on flange fitting (such as fitting 55 shown in FIG. 5A). The fitting 55 is described in U.S. Pat. No. 4,968, entitled “Bolt-On Flange”, assigned to the assignee of the present invention. The bolt-on flange fitting facilitates ease of maintenance and cleaning of the tank interior and diffuser nozzles.

The presence of the diffuser nozzles 45, 47, at the cold water inlet 29 and the hot water circulation return inlet 35 pulls relatively coldest water from a bottom region of the tank interior with the water being reintroduced to the tank interior from the hot water circulation return inlet 35 at a higher relative location. In other words, the diffuser nozzles 45, 47, direct the flow of water outward and downward, thereby minimizing any disturbance of heated water in the top region of the tank. Because of the way the return water is directed and distributed, the presence of the diffuser nozzles 45, 47, prevents disturbing a naturally occurring stratification of heat, providing a more uniform tank temperature as well as ensuring the heat exchanger is provided with the coldest inlet water, thereby increasing the efficiency of the system.

The indirectly heated, storage water heater system of the invention also includes an electronic controller which is operated so that the control of steam supplied to the system and flow of water through the heat exchanger 11 ensures that steam is only present in the heat exchanger when there is a predetermined high flow rate of water.

The electronic controller, which is illustrated schematically as 57 in FIG. 1, controls both the circulating pump 37 and condensate control valve 21 in response to temperature measurements taken from the temperature sensor 59 located in the tank interior 27. FIG. 4 is a flow chart of the relatively simple control circuit logic that can be employed in controlling the system.

In an initial state, the heat exchanger, water storage tank and associated plumbing are at ambient or ground water temperatures. The system is first subjected to a startup cycle in which power is applied to power the system and provide a control signal for the water heating system's operation

The “start” point on the flow chart 61 represents the point at which it has been determined that the system is full of potable water and air has been removed from the water storage tank and at which point steam is to be supplied to the heat engine. When power is supplied to the electronic controller 57, a reading is taken from the temperature sensor 59 located in the tank interior 27, the step of reading the temperature being shown as step 63 in FIG. 4. Demand for hot water causes cold makeup water to enter the storage tank through the cold water inlet 29, thus reducing tank temperature. If the temperature reading from the sensor 59 shows the water temperature at the sensor location to be below a given predetermined set point, the circulation pump 37 is turned on by the controller and the condensate control valve 21 is provided power. This begins circulation flow to the heat engine and opening of the condensate control valve, as illustrated by the steps 65, 67, in FIG. 4. The colder domestic water flowing through the heat exchanger 11 extracts heat from the steam causing the steam to condense. This condensate is evacuated from the heat exchanger 11 through the steam trap 23 (see FIGS. 2 and 3). The pressure drop caused by condensing steam allows more steam to enter the exchanger During the call for heat portion of the heat exchange cycle, water is circulated at a predetermined flow rate to the heat exchanger 11 to extract latent heat from the steam being supplied to the heat exchanger, while also providing a relatively small degree of sub-cooling, thereby causing a flow of condensate on the steam side of the heat exchanger while drawing more steam through the system. Circulating water returns to the water storage tank interior through the hot water circulation return inlet 35 and diffuser nozzle 47, causing the temperature of water in the water storage tank to rise. The use of the diffuser nozzle 47 causes stored water to fill from the top of the water storage tank until the temperature sensor located in the tank interior reaches the desired set point. Once the set point is reached, the electronic controller 57 immediately removes power from the condensate control valve 21 in step 69, as the circulating pump 37 continues to run on a time delay shutoff.

When demand for hot water ends, the tank will return to set point temperature due to the heated water exiting the heat exchanger. When the proper tank temperature is reached, the temperature sensing probe 59 signals the condensate control valve to close. This traps condensate in the heat exchanger. The pump remains energized temporarily to extract residual heat from the heat exchanger and transfer it into the domestic water. The heat exchanger 11 has internal surfaces (as at 13 in FIG. 1), and the continued running of the circulating pump 37 causes the heat exchanger to flood with condensate until all heating surfaces are in contact with the condensate, the condensate then being cooled below the point of scale formation, Steam continues to condense until the exchanger is entirely filled with condensate and the flow of steam is thereby stopped completely. Continued domestic water flow then extracts the sensible heat from the condensate.

After a predetermined time period (one minute in step 71 in FIG. 4), power is removed from the circulating pump 37 (in the step 73 in FIG. 4) and the system is then effectively in a standby state (as shown at 75 in FIG. 4), awaiting the next demand for hot water. Delayed pump operation may increase the tank temperature by 1 to 2 degrees F. As supplied domestic potable water is used, cold water flows into the water storage tank interior through the cold water inlet 29 and then passes through the cold water inlet diffuser 45, the relatively colder water entering the diffuser causing water to fill the tank from a bottom region to a top region. When the level of cold water in the tank interior 27 reaches the location of the electronic controller temperature sensor 59, the electronic controller 57 will provide power to the circulating pump 37 and condensate control valve 21, beginning the heating cycle again.

An invention has been provided with a number of advantages. The control of the steam system and flow through the water side of the exchanger ensures that steam is only present in the heat exchanger when there is a high flow rate of water. This reduces the formation of scale during idle cycles, but also help to ensure that any scale formed is quickly washed away from the heating surfaces. In addition, by flooding the exchanger with condensate, there is no loss of pressure on the heat exchanger. This will minimize the pressure fluctuations. Since the condensate must be pushed out at the beginning of a call for heat, the tubes are gradually reintroduced to steam, minimizing the effects of thermal shock. In combination, this will prolong the life of the heat exchanger.

The tank design ensures that the circulation of water does not mix the contents of the entire tank during pump operation. With the installed diffuser nozzles, the coldest water is pulled from the bottom of the tank and reintroduced in at a higher location. The diffuser nozzle at both the cold water inlet and the hot water recirculation inlet reduce the velocity and direct the flow of water outward and downward. This minimizes disturbance of the heated water in the top of the tank. By directing the heater water from the exchanger downward, it causes the inlet water to be mixed with the cooler water at the bottom of the tank helping to prevent overheated water from “stacking” in the tank. In the same way, the diffuser on the cold water inlet to the tank minimizes the effect of large water draws from disturbing the heated water above it and help to ensure the coldest water is available to the heat exchanger, thereby increasing efficiency. Through the use of this combination of circulation control and tank diffusers, the outlet temperature and stratification of the tank show a close to ideal temperature distribution, even with drastically differing flow rates.

While the invention is shown in only one of its forms, it is not thus limited and is susceptible to various changes and modifications without departing from the spirit thereof. 

What is claimed is:
 1. A system for providing potable, domestic hot water using an indirectly heated, storage water heater system, the system comprising: a heat engine package comprising a steam operated heat exchanger, a temperature operated pump and a condensate control valve; a storage package including a water storage tank with an internal temperature sensor, the water storage tank being located apart from but plumbed to the steam operated heat exchanger, and an electronic controller operatively associated with the temperature sensor in the water storage tank, the temperature operated pump, and the condensate control valve to control the supply of steam to the heat exchanger and the discharge of condensate therefrom, as well as the flow of hot and cold water to and from the water storage tank; wherein the water storage tank has an interior, a cold water inlet and a cold water circulation outlet connected by a conduit to one side of the heat exchanger, a hot water circulation return inlet for communication with the heat exchanger for directing an inlet stream of hot water from the steam operated heat exchanger back into the storage tank interior, and a hot water outlet, and wherein a diffuser nozzle is located within the tank interior at both the cold water inlet and the hot water circulation return inlet to reduce velocity and directionality of the inlet stream of hot water being introduced into the tank interior from the heat exchanger; wherein the electronic controller is operated so that the control of steam supplied to the system and flow of water through the heat exchanger ensures that steam is only present in the heat exchanger when there is a predetermined high flow rate of water.
 2. The system of claim 1, wherein the presence of the diffuser nozzles at the cold water inlet and the hot water circulation return inlet pull relatively coldest water from a bottom region of the tank interior with the water being reintroduced to the tank interior from the hot water circulation return inlet at a higher relative location, the diffuser nozzles directing the flow of water outward and downward, thereby minimizing any disturbance of heated water in a top region of the tank.
 3. The system of claim 2, wherein the heat exchanger is a shell and tube heat exchanger with a shell side and a tube side, with relatively cooler water to be heated being passed on a selected one of the shell and tube side of the heat exchanger and steam being passed on a remaining side of the heat exchanger, the steam being supplied from a suitable steam source;
 4. The system of claim 3, wherein the diffuser nozzles are mounted on an exterior surface of the water storage tank by a bolt on flange fitting which facilitates ease of maintenance and cleaning of the tank interior and diffuser nozzles.
 5. The system of claim 3, wherein the presence of the diffuser nozzles prevents disturbing a naturally occurring stratification of heat, providing a more uniform tank temperature as well as ensuring the heat exchanger is provided with the coldest inlet water, thereby increasing the efficiency of the system.
 6. A method for providing potable, domestic hot water to an end user, using an indirectly heated, storage water heater system, the method comprising the steps of: providing a heat engine package comprising a steam operated heat exchanger, a temperature operated circulating pump and a condensate control valve; providing a storage package including a water storage tank with an internal temperature sensor, the water storage tank being located apart from but plumbed to the steam operated heat exchanger, and an electronic controller operatively associated with the temperature sensor in the water storage tank, the temperature operated pump, and the condensate control valve to control the supply of steam to the heat exchanger and the discharge of condensate therefrom, as well as the flow of hot and cold water to and from the water storage tank; wherein the water storage tank has an interior, a cold water inlet and a cold water circulation outlet connected by a conduit to one side of the heat exchanger, a hot water circulation return inlet for communicating with the heat exchanger for directing an inlet stream of hot water from the steam operated heat exchanger back into the storage tank interior, and a hot water outlet, and wherein a diffuser nozzle is located within the tank interior at both the cold water inlet and the hot water circulation return inlet to reduce velocity and directionality of the inlet streams of water being introduced into the tank interior; wherein the electronic controller is operated so that the control of steam supplied to the system and flow of water through the heat exchanger ensures that steam is only present in the heat exchanger when there is a predetermined high flow rate of water.
 7. The method of claim 6, wherein in an initial state, the heat exchanger, water storage tank and associated plumbing are at ambient or ground water temperatures and wherein the system is first subjected to a startup cycle in which power is applied to power the system and provide a control signal for the water heating system's operation.
 8. The method of claim 7, wherein once it has been determined that the system is full of potable water and air has been removed from the water storage tank, steam is then be supplied to the heat engine.
 9. The method of claim 8, wherein when power is supplied to the electronic controller, a temperature sensor associated with the controller senses that water in the water storage tank is below a given set point, the electronic controller then supplies power to the temperature operated circulating pump and to the condensate control valve beginning circulation flow to the heat engine and opening the condensate control valve.
 10. The method of claim 9, wherein the heat exchanger is a shell and tube heat exchanger with a shell side and a tube side, with relatively cooler water to be heated being passed on a selected one of the shell and tube side of the heat exchanger and steam being passed on a remaining side of the heat exchanger, the steam being supplied from a suitable steam source.
 11. The method of claim 10, wherein water is then circulated at a predetermined flow rate to the heat exchanger to extract latent heat from the steam being supplied to the heat exchanger, while also providing a relatively small degree of sub-cooling, thereby causing a flow of condensate on the steam side of the heat exchanger while drawing more steam through the system.
 12. The method of claim 11, wherein circulating water returns to the water storage tank interior through the hot water circulation return inlet and diffuser nozzle, causing the temperature of water in the water storage tank to rise.
 13. The method of claim 12, wherein the user of the diffuser nozzle on the hot water circulation return inlet causes stored water to fill from the top of the water storage tank until and temperature sensor located in the tank interior reaches a desired set point, and wherein once the desired set point is reached, the electronic controller immediately removes power from the condensate control valve as the circulating pump continues to run on a time delay shutoff.
 14. The method of claim 13, wherein the heat exchanger has internal heating surfaces, and wherein continued running of the circulating pump causes the heat exchanger to flood with condensate until all heating surfaces are in contact with the condensate, the condensate then being cooled below the point of scale formation, and wherein once the predetermined time delay has been reached, power is removed from the circulating pump and the system is in a standby state.
 15. The method of claim 14, wherein as supplied domestic potable water is used, cold water flows into the water storage tank interior through the cold water inlet diffuser, the relatively colder water entering the diffuser causing water to fill the tank from a bottom region toward a top region.
 16. The method of claim 15, whereby, when the level of cold water in the tank reaches a location of the electronic controller temperature sensor, the electronic controller will provide power to the circulating pump and condensate control valve, beginning the heating cycle again. 